Means for making electrostatic prints



March 11, 1958 G. P. GRANT, JR 2,826,168

MEANS FOR MAKING ELECTROSTATIC PRINTS Filed April 16, 1956 2Sheets-Sheet l ATTOENE 7 5.

March 11, 1958 G. P. GRANT, JR 2,326,168

MEANS FOR MAKING ELECTROSTATIC PRINTS I Filed April 16, 1956 2Sheets-Sheet 2 4 INVENTOR.

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United States Patent- MEANSFOR MAKING-ELECTROSTATIC PRINTS Garnet PeterGrant, Jr., Olmsted Falls, Ohio, assignor to Grant Photo Products, Inc.,Cleveland, Ohio, a corporation .of Delaware Application April 16, 1956,Serial No. 578,275

15 Claims. (Cl. 118--637) This invention relates to means for; makingelectrostatie prints;

Electrostaticprinting systems are known, but in the.

has usually been found to be preferable to the accomplishment of theseends.-

The present invention consists in and has for its principal object theprovision of ways and means for carrying outthe various steps, exclusiveof exposure to light,;,-- in;one; and the same apparatus. With that inmind,. the invention contemplates a machine which incorporates means forcutting the print to the desired size, applying'the electrical charge.to it, supplying the pigmentrequired to develop the latentimage, andfixing the image by heat. According to the present invention, all of thestated functions, not including exposure of the print to light,- areperformed in a single machine which is at once compact, sturdy, and easyto service.

Other objects, advantages and features of the invention will be apparentfrom the. description which follows and-from the accompanying-drawings,in which:

Figured is a frontelevation of the machine of the present invention.

Figure 2 is an isometric of the machine showing the parts'as they wouldappear with the near side wall partially broken away.

Figures.3 to 6 are sections with certain parts in elevation seen as iffrom line 33 of Figure 1.

Figure-7 is a section with certain parts in elevation seen as if fromline 7-7 of Figure 1.

Figure 8 is a view similar to Figure 2 showing a modification in whichthe more important operations are performedsautomatically.

Figure 9 is a plan of the machine of Figure 8 with the top of thehousingbroken away as indicated by lines 9'9 of Figure 8.

Figure 10- is an enlarged detail showing in elevationcertain'ofthecomponents appearing in Figure 8.

Figure 11 is a section with certain parts in elevation seen as if fromline-llll-of Figure 9.

In'the'embodiment of the invention shown in Figures 1 to 7, themechanism making up the machine is enclosed withga metal housing 1provided with an entry slot 2 and an exit slot 3, the two'slots beingdefined by walls 2ag 2 b and 3a, 3b, respectively. Within the housing isa cylindrical metal drum 4 mounted for rotation about a Over roughly theupper half of its periphery,-drum 4 is encompassed by a stationary metalshield 5 of generally semi-cylindrical shape one end or transverse-edgeof-whichis attached-to the rear end of 2,826,168 Patented Mar. 11, 1958housing 1 and the other end or transverse edge of which is attached tothe lower end of wall 2a of entry slot 2.

Directly beneath-drum 4 is a horizontal partition 6 of which the nearand far edges, seen as in Figure 2, are attached in anyconvenientfashion to the sidewalls of housing l. To the inner transverse edge ofpartition 6 is rigidly attached'a vertical partition 7. At its upperend, partition 7 is affixed to the upper end of wall 3a of. exit slot},the two terminating below the central horizontalplanemf the machine justabove the point where they engage each other. Thus neither wall 3:: ofexit slot 3 norvertical partition 7 blocks the exit slot at its upperend, which stands in communication with theinterior of the machine.Horizontal partition 6 is used to support a tray 8 containing a finelydivided pigment of the type-commonly employed in electrostatic printing;below it is a shallow chamber 9 in which is contained the power pack 10.Access to power pack 10 maybe had through a door 11 hinged as at 12 tothe wallforming part of, the housing at the rear end of the machine.

At the front end of the machine is a second door 13 pivoted on verticalhinges 14. Door 14 provides access to that portion of the machinebetween slot walls 2b and 3b, in which is housed a supply roll 15 of amaterial (usually paper) that is used as hereinafter explained in makingprints. Supply roll 15 is mounted on a rod 16 extending transversely ofthe machine between its two longitudinally extending side walls. Thepaper is withdrawn from supply roll 15 in the form of a continuous web17; passes downward to anunderlying direction-changing roller 18, andthen proceeds in a horizontal plane to and through ahorizontallyextending openingin the frontend of the housing justaboveexit slot 3. Immediately after leaving roller 18, the paper passes"beneath an electrically charged wire 19 carrying high voltageelectricity, the current therefor being supplied from power pack 10 bysuitable connections (not shown). At this stage, web 17 acquires anelectrostatic charge, this'asa result of passing closely beneath wire19.

On its way out of housing 1, web 17 proceeds between two nip rollers 20,one of which is rotated by means of a crank 22 provided with a handle22a (Figure-2). As it proceeds through the opening in housing 1, 'web 17passes through a correspondingly slotted block 23 that is rigidlyaffixed to housing 1 immediately below door-13. Supported injuxtaposition to the slot in block 23 is a guillotine knife 24 that isprovided with a handle 25 by which the body of the knife 24 may beraised and lowered. The knife is so pivoted on block 23 that handle 25describes an are about pivot pin 26. It may be-raised as high asrequired, but is precluded by a stop 27 on-block 23 from dropping belowthe horizontal position: i see Figure 1. With the knife raised, thedesired length of material is withdrawn from supply roll 15, after whichthe knife is urged downward with the aid'of handle- 25 to provide a cutsheet 28. In the latter, the=electrostatic charge imparted by wire 19 toweb 17 is substantially unimpaired.

Sheet 28 is then exposed through a negative of any suitable sort to forma latent image on top face 28a. The latter will already have beensensitized; i. e., prepared for the production of the image, bysurfacing it in suitable fashion before the material from which it iscut is wound to form the supply roll. sensitizing procedures of thissort are well known in the electrostatic printing art. The exposure toproduce the image may be accomplished in any one of a variety of ways,as in a hand-held printing frame, an automatic printing machine, amachine-for exposing blueprints, etc. The effect ofexposing top face 28aof sheet-28 to the light transmitted through the-negative is to modifythe electrical chargein a pattern determined by the negative, therebypreparing the sheet for processing in a machine of the kind described inthe present application. Although the electrical charge may have beenvery extensively modified in the meanwhile, the sheet itself appearsunchanged to the eye.

Thereafter, sheet 28 is inserted in slot 2 with its top face 28a next towall 2a of entry slot 2. Immediately before this is done, drum 4 shouldbe re-positioned within to the apparatus as a whole in such manner thatthere will be assurance of substantial alignment between exit slot 2 anda shallow slot 29 extending lengthwise of drum 4 in parallelism to itsaxis. Alignment of slot 29 with entry slot 2 can be and preferably isindicated by a signaling system of a suitable kind, such signalingsystem operating only when alignment is present. Once such alignment hasbeen achieved, it becomes possible by urging sheet 28 into slot 2 toengage the leading end of the sheet in slot 29.

In the embodiment of the invention shown in Figures 1 to 7, thesignaling sytem as a whole responds to the position of a lug 30 on thenear end face of drum 4 (Figure 2). Lug 38 is so located that it cancooperate with a microswitch 31 on housing 1 (Figure l). Preferably,such switch is of the type adapted for momentary actuation; if actuated,it operates to close a circuit which includes a lamp assembly 32 mountedon the inside of the top of housing 1 just below a window 33 of thejewel type. Whenever the switch is engaged by lug 30, the lamp in lampassembly 32 will be illuminated; in other words, the lamp will flashonce for each 360 of rotation of drum 4. It will remain illuminated onlyso long as there is substantial alignment between entry slot 2 and slot29 in drum 4 (Figure 3).

With the parts as represented in Figure 3, the lamp in lamp assembly 32is illuminated, slots 2 and 29 are in alignment, the leading end 34 ofsheet 28 projects out of -slot 2 into slot 29, and the trailing end 35of sheet 28 is in the vicinity of the entrance end of slot 2.

Drum 4 is mounted on a shaft 36 that extends from the near side to thefar side of the housing as seen in Figure 2. At its near end, shown inelevation in Figure 2, shaft 36 carries a knob 37 provided with anindicating arrow that points up when the lamp in lamp assembly 32 isilluminated. Just inside the near wall of housing 1, shaft 36 mounts apulley 38 connected by a belt 39 to a second pulley 40 of smallerdiameter. Pulley 40 is mounted just inside the near wall of the housingat the inner end of a crank 41 so positioned that its shank passesthrough the wall. Crank 41 is provided with a handle 41a by which it,pulley 38 and drum 4 may be rotated in unison.

With the parts in the position shown in Figure 3, clockwise rotation ofcrank 41 serves to rotate drum 4 in the clockwise direction. Drum 4draws sheet 28 with it by virtue of the engagement of the leading end ofthe sheet in slot 29. The trailing end of the sheet is constrained byshield to follow the surface of the drum as the latter revolves aboutthe axis of shaft 36. By the time crank 41 has been turned sufficientlyto produce about 300 of rotation of drum 38, which state of affairs isshown in Figure 4, the leading end 34 of sheet 28 has been pulled into,through, and out of tray 8. Trailing end 35 has not yet been pulledthrough tray 8 but is still in the area in which shield 5 exercises itsrestraining action on the sheet.

Continued rotation of crank 41 brings drum 4 and sheet 28 into thepositions shown in Figure 5, in which both the leading and trailing endsof the sheet are free of the tray. By this time, drum 4 has made one anda half revolutions, in the course of which the lamp in lamp assembly 32has flashed twice, once at the outset and once after 360 of rotation.The angular position of the drum, measured radially, is revealed by thearrow on knob 37 on shaft 36, which at this stage points down.

While sheet 28 is being drawn through tray 8, it comes into intimatecontact with a powdery pigment 43 of one of the kinds conventionallyemployed in making electrostatic prints. Pigments of this sort may varyconsiderably in composition but in a typical case may contain ironfilings, carbon black and a finely divided thermoplastic resin thatfuses at moderate temperatures. The pigment mixture is picked up bysheet 28 as it follows the course already described through tray 8. Itattaches itself to those parts of sheet 28 in which the latent image hasbeen formed by exposure of the sheet to light. Thus the pattern of thenegative is reproduced in positive fashion on sheet 28.

In order to keep pigment 43 thoroughly mixed, vanes 44 are provided intray 8, each of them being pivoted at each of its two ends to theadjacent portion of the tray. Near their upper ends, vanes 44 areinterconnected by two links 45, one at the near end of the tray and oneat the far end. Links 45 are provided in order to move vanes 44 inunison. Occasional movement of the vanes at irregular intervals issufiicient.

To introduce such movement, the far end of the tray; i. e., the sideseen in Figure 7, is provided with an upright lever 46 that is pivotedat 46a to a bracket 47 on the tray Wall. At its lower end, lever 46makes a pin and slot connection with the underlying link 45, suchconnection being indicated at 48 (Figure 7). A coil spring 49 connectedat one end to the tray itself biases lever 46 toward shaft 36.Periodically it is urged away from shaft 36 by a cam 50 which is fixedto and rotates with the shaft.

The parts having respectively attained the positions shown in Figure 5,the next step is to remove sheet 28 from the machine. This is done byreversing the direction of rotation of crank 41, which results inmovement of pulleys 38 and 40 in the counterclockwise direction. Inorder to disengage the trailing end 35 of sheet 28 from the drum, themachine is provided with a deflector 51 fastened to a pivoted rod 52extending transversely through housing 1. Deflector 51 may consist of asingle blade extending all the way across the housing or of a series ofspaced fingers, the latter being the prefen'ed construction. Normally;i. e., during clockwise rotation of drum 4, deflector 51 will standupright, as indicated in Figures 3 to 5.

When, however, it is desired to reverse the direction of rotation torelease sheet 28 from the drum, deflector 51 is moved into the inclinedposition shown in Figure 6, this being done by moving an arm 53 attachedto rod 52 on the outside of the housing. Thereafter, whencounterclockwise rotation of drum 4 is initiated, the trailing end 35 ofsheet 28 is bodily deflected from the surface of the drum, preventing itfrom coming into renewed contact with the pigment 43 in tray 8. Instead,sheet 28 moves downwardly between two adjacent discharge rollers 54 and55 in the manner indicated by the arrow in Figure 6.

On the far side of the machine; i. e., the side at the left in Figure 1,discharge rollers 54 and 55 are equipped with intermeshing gears 54a and55a. Gear 55a is driven by a pulley 56 that is coupled by a belt 57 to alarger pulley 58 on shaft 36. Thus when drum 4 (indicated in dottedlines in Figure 7) is rotated in the counterclockwise direction, theupper surfaces of rollers 54 and 55 move toward each other in suchmanner as to encourage sheet 28 to enter into the bight between them. Ifdrum 4 is rotated in the clockwise direction, rollers 54 and 55 rotatein the reverse directions without doing any harm.

In order to fuse the pigment which adheres to sheet 28 Where the latentimage has been formed, a heating unit 59 is located on the exit side ofrollers 54 and 55 in approximately the position shown in Figure 2. Alongwith suitable leads (not shown), heating unit 59 incorporates areflector 60 and an electrical heating element 61. It is adapted toproduce a degree of heat sufficient to fuse the fusible components ofthe pigment which adheres to sheet 28, thus fixing the image. This isdone gradually as the print is propelled through rollers 54 and 55.Ultimately, the print drops down into exit slot 3, which acts as areceptacle, from which the print can easily be removed.

A modification. in which certain .of the operations that would otherwisehave to be performed by hand are performed automatically is shown inFigures 8 tell. In such modification, housing 71has 'anxentry slot 72and an .exit slot 73 arranged'much, as in the previously describedembodiment of the invention. Within, housing-71 is a drum 74 providedwith a transverse slot 75 in its periphery. Drum 74 is mounted on ashaft 76 that extends across the machine from the near side to-the farside, seen as in Figure 8.

Below drum 74 is a horizontalpartition 77 on which is mounted a tray 78for pigment 79. A vertical partition 80 adjoins horizontal partition 77to provide therebelow a shallow chamber 81 in which is received thepower pack 82. Access to tray 78 and power pack 82 may be had through adoor 83 hinged to the housing as at 84. At the left hand end of themachine as a whole, seen as in Figure 8, is a door 85 similar to thedoor 13 of the previously described embodiment of the invention.Accessible through door 85 is a supply roll 86 containing the materialthat is to be made into prints. The material proceeds in web formbeneath a charged wire 87 to and between nip rollers 88, one of which isturned manually by a crank 89 provided with a handle 89a. After leavingnip rollers 88, the web passes through a suitable opening in the frontend of the housing. It is severed by means of knife 90 to form a cutsheet 91 of the desired length.

After being exposed to light as already described, sheet 91 isintroduced. into entry slot 72 with its sensitive top face 9.1a adjacentupper slot wall 72a. Its leadingedge is engaged in transverse slot 75 indrum 74, which is so synchronized with the rest of the apparatus thatwhen the parts are in the position shown in Figure 8, transverse slot 75is always in juxtaposition to the entry slot. By means of a smallsprocket 92, a chain 93 and a large sprocket 94, the diameter of thelarge sprocket being fifty percent greater than that of the smallsprocket, drum 74 may be driven from a pinion 96 on a stub shaft 95.Pinion 96is connected through an intervening gear train to a similarpinion 97 on the shaft 98a of an electric motor 98 (Figures 8 and Asbest seen in Figure 10, pinion 97 meshes with a gear 99 mounted on astub shaft 100. This shaft is encompassed on one side of gear 99 by asleeve 101 to which is rigidly afiixed a plate 102 of generallytriangular shape. On the far side of the plate 102, in alignmentwithgear 99, are three small gears 103, 104 and 105. These gears aremounted on stub shafts on plate 182; therefore, they always bear thesame relationship to each other. However, the mounting plate itself isso arranged that the drive may be from gear 99 to gear 103 to gear 104and thence to gear 96 or, alternatively, from gear 99 to gear 103 togear 104 to gear 105 and thence to gear 96.

Whether gear 104 or gear 105 engages gear 96 depends on the position ofthe plate 102. With the parts in the positions shown in Figure 10, gear105 is an ineffective idler. On the other hand, when this plate isrotated a few degrees to the left of the position shown in Figure 10,gear 104 is disengaged from, and gear 105 is engaged with, pinion 96. Inthelatter case, neither gear104 nor gear 105 serves as an idler. Theinterposition of gear 105 in such case operates to reverse the directionof rotation of pinion 96 and large sprocket 94.

On large sprocket 94 is lug 107, seen in Figures 8 and 10, that isadapted to engage a microswitch 108 of the maintained-contact type(Figure 9). Switch 108 is mounted on housing 71 in a position in whichlug 107 can, from time to time, make contact with it, thus moving themoveable switch contact from open to closed position or vice versa.Wires 109 from switch 108 lead to a solenoid 110 mounted on the base ofhousing 71 in the manner indicated in Figure 8. Solenoid 110incorporates a plunger 111 mounted on a rod 112 which is pivotallyconnected to a lever 113 that is itself rigidly mounted on sleeve 101.Lever 113, rod 112 and plunger 111 are biased toward theposition shownin Figure 10 by means of a coil spring 114.

Coupled to lever 113 at its right-hand end, seen. as in Figure 8, is alink 115 which'carries a deflector 116 operating on, the bell-crankprinciple. It is fastened to a pivotally mounted rod similar to rod. 52(Figures 2 to 7). So long as the other parts are in the positions shownin Figures 8 and 10, it is out of contact with drum 4. ,As representedin Figures 8 and 10, the moveable contact in switch 108 has just beenmoved into opencircuit position by action of lug 107. Therefore,solenoid 110 is de-energized, the rotation of the pinions, gearsand-sprockets is as shown by the arrows in Figure 10, anddrum 74 isrotating clockwise; Engagement of drum '74 by deflector 116 :is notdesired under these conditions.

Inasmuch as clockwise rotation of small sprocket 92 results fromclockwise rotation of large sprocket 94, which is half again as large indiameter, drum 74 makes one and one-half clockwise revolutions for eachclockwise revolution of large sprocket 94. Thus after: lug 107 oncemoves the moveable contact in switch 108 into the open circuit position,the leading end of sheet 91 will be carried 540 around the axis ofrotation of drum 74 before the lug again makes contact with switch 108.I At this time, the leading end of the sheet is in a positioncorresponding to the leading end of sheet 28 in Figure -5 of thedrawings dealing with the previously described embodiment of theinvention. It is only when sheet 91 reaches this position that lug 107re-engages switch 108 to cause the moveable contact of the switch tosnap into the closed-circuit position.

When this happens, solenoid 110 is energized, thus drawing plunger 111and plunger rod 112 into their retracted positions. This movementdepresses the lefthand end and elevates the right-hand end of lever 113,seen as in Figure 10, which in turn rotates sleeve 101 and plate 102 afew degrees to the leftabout the axis of stub shaft 100. -Thus gear 105is cut into operation, after which the drive is from pinion 97 to gear99 to gear 103 to gear 104 to gear 105 to pinion 96, which now turnscounterclockwise. Counterclockwise movement of gear 96 producescounterclockwise movement of sprocket 94, chain 93 and sprocket 92,which in turn produces counterclockwise movement of drum 74.

At the same time, elevation of the right-hand end of lever 113 forcesdeflector 116 into engagement with the surface of drum 74. After thishappens, it is in a position to deflect what was originally trailing endof sheet 91 exactly as in the case of sheet 28 in the embodiment of theinvention already described. Under the influence of the counterclockwisemovement of drum 74, sheet 91 then passes between exit rollers 128 and129 (Figure 9) and thence past heating unit 130 (Figure 8). The latteris operated from leads 131 (Figure 9). As the sheet is propelled pastheating unit 130, the pigment fuses to give the desired permanent image.The sheet when released by rollers 128 and 129 drops down onto lowerwall 73a of exit slot 73, from which it can readily be retrieved.

To reveal the position and direction of rotation of drum 74 at a giventime, a signaling system of any suitable kind may be provided.

During the time when drum 74 is rotating in the clockwise direction, itcarries sheet 91 into and through the pigment 79 in tray 78. In theembodiment of the invention shown in Figures 8 to 11, vanes are not usedto keep the pigment mixed; instead, three magnetized rolls 117 apply thepigment to the exposed surface of the sheet. Rolls 117 are positivelydriven by sprockets 118 at the far end of the machine (Figure 11).Sprockets 118 are driven by a chain 119 which is itself driven by alarge sprocket 120 on a rotatable stub shaft 121. Sprockets 118 and 120and chain 119 are in a common plane adjoining the far side wall ofhousing 71; see Figure 9.

Shaft 121 is driven by means of a gear 122 that is in engagement with apinion 76a on shaft 76 in the space between sprocket 120 and theadjacent end of drum 74.

Shaft 76, through pinion 76a and gear 122, also drives a gear 123, whichin turn drives a gear 124. Shaft 76 is journaled in a bracket 125 onwhich are mounted stub shafts carrying gears 123 and 124. These twogears form part of the gear train communicating power to the exitrollers. Gear 124 drives the nearer of two meshing gears 126 and 127,one at the end of exit roller 128 and the other at the end of exitroller 129. The shafts carrying exit rollers 128 and 129 are journaledin bracket 125: see Figure 9. Below the exit rollers on the upper wall73b of exit slot 73 is the heating unit 130, indicated in Figure 9 indotted lines, to which electricity is supplied by leads 131.

The foregoing description and the accompanying drawings set forth twoillustrative embodiments each of which in its own way incorporates someof the novel features of the present invention. One of theseembodiments, that illustrated in Figures 1 to 7, is essentially ahand-operated machine; the other, that illustrated in Figures 8 to 11,is essentially automatic in operation, requiring little more than manualactuation and de-actuation of an electric motor. In addition thereto,other embodiments will suggest themselves, for it is apparent thatchanges in either or both of these embodiments may be made by thoseskilled in the art without departing from the spirit of the invention.

It is intended that the patent shall cover, by summarization in appendedclaims, all features of patentable novelty residing in the invention.

What is claimed is:

1. Apparatus for processing electrically charged sheet materialcomprising a housing; a drum within the housing adapted for rotation inclockwise and counter-clockwise directions; means associated with thehousing for feeding sheet material to the surface of the drum; means forapplying powder to the sheet material, said means including a powderreservoir at the bottom of the housing; means for separating the sheetmaterial from the surface of the drum during the movement of the drum inone of said directions; and, acting on the sheet material leaving thedrum, means for subjecting the sheet material to the action of heat.

2. Apparatus for processing sheet material as in claim 1 in which thedrum is provided with means engaging the leading edge of the sheet.

3. Apparatus for processing sheet material as in claim 2 in which themeans engaging the leading end of the sheet takes the form of a slot inthe drum.

4. Apparatus for processing sheet material as in claim 3 in which thehousing incorporates an internal shield for guiding the trailing end ofthe sheet.

5. Apparatus for processing sheet material as in claim 4 in which thehousing incorporates selectively positioned means for deflecting thetrailing end of the sheet from the surface of the drum.

6. Apparatus for processing an electrically charged print comprising adrum; means for attaching the print to the surface of the drum; meansfor imposing on the drum rotary movement first in one direction and thenin the opposite direction; means including a powder reservoir beneaththe drum for applying a powder to the exposed surface of the printduring rotation of the drum; means for detaching the print from thesurface of the drum during rotation of the drum; and means for guidingthe print away from the drum.

7. Apparatus as in claim 6 in which the drum is provided with meanslimiting its movement in the first direction.

8. Apparatus as in claim 6 in which the drum is provided with meanslimiting its movement in the opposite direction.

9. Apparatus as in claim 6 in which the drum incorporates a system ofgearing for limiting movement of the drum in either direction.

10. Apparatus for processing electrically charged sheet materialcomprising a container; a drum in the container; means for rotating thedrum first in one direction and then in the opposite direction; meansfor engaging a sheet of electrically charged material with the drumduring movement of the drum in the first direction; means fordisengaging said sheet of electrically charged material from the drumduring movement of the drum in the opposite direction; and means forapplying a powder to said sheet of electrically charged material whilethe drum is being rotated in the first direction, said means including apowder reservoir in proximity to the bottom of the drum.

11. Apparatus as in claim 10 in which the means for engaging the sheetof electrically charged material with the drum comprises a slot in thedrum into which the leading end of the sheet of electrically chargedmaterial is introduced.

12. Apparatus as in claim 10 in which the means for disengaging thesheet of electrically charged material from the drum comprise one ormore deflectors which are maintained out of contact with the drum duringmovement of the drum in said first direction but which are maintained incontact with the drum during movement of the drum in the oppositedirection.

13. Apparatus as in claim 12 in which the deflectors take the form ofspaced fingers disposed at intervals across the surface of the drum.

14. Apparatus as in claim 13 in which the fingers are pivoted in suchmanner that they can be swung into and out of contact with the surfaceof the drum.

15. Apparatus as in claim 14 in which the pivoted movement of thefingers is coordinated with the movement of the drum.

References Cited in the file of this patent UNITED STATES PATENTS126,097 Shoop Apr. 23, 1872 835,883 Fritsche Nov. 13, 1906 2,221,776Carlson Nov. 19, 1940 2,297,691 Carlson Oct. 6, 1942 2,624,652 CarlsonIan. 6, 1953 2,626,865 Mayo et al. Jan. 27, 1953 2,701,765 Codichini eta1 Feb. 8, 1955

